A Boeing display model from the late 1980s with some sort of airbreathing cruise missile. I'm guessing scramjet powered due to the sizable solid rocket booster.
Anybody know what it is?
Pretty much exactly what you (should) think it is.
The powerplant evolved from earlier work on the low level run in to target concept. From "Lightning Bolts":
"To remain effective, LLRI would have to add terminal propulsion and increase stealth features, causing the cost per vehicle to increase sharply"
This was in reference to countering the SA-10. The vehicle in OBB's image is not a MARV in the classic sense - it's exactly what you would think it was - but this concept had terminal air breathing propulsion that evolved from earlier work on the powered LLRI concept.
The carrier aircraft should be interesting, mostly because it's NOT a B-52.